1. Field of the Invention
The present invention relates to a method and apparatus for detecting the position of an abnormal site such as a crack, in a pipe buried beneath the ground surface.
2. Description of the Related Art
A pipe, such as a metal pipe, is used to allow passage of a fluid, such as a gas, oil, chemicals, potable water, or a liquid such as sewage water. If there occur an abnormal site such as a crack in this type of pipe, then a fluid leaks at these sites, thus causing a waste of valuable resources. It is of advantage from the standpoint of the effective utilization of the resources to detect and repair such a leak-of-fluid site or sites. Some pipes are buried or laid beneath the ground surface and it is, therefore, difficult to locate such a site or sites from the surface of the ground.
This problem will be explained below, in more detail, in conjunction with the detection of a site of a leak, into the ground, of water running through a water service pipe or main for instance. Usually, the water service pipe is buried or laid underneath the ground surface and, if there occur cracks or broken sites in the water pipe due to their being worn out etc., with the passage of time, water leaks out of such sites on the water pipe. Water permeated or penetrated, as leak water, out of the water pipe into the ground often reaches a huge amount as a whole. In the dry season, the shortage of water becomes a grave social problem in recent times. It is, therefore, very important, from the standpoint of acquiring the water resources, to make the leak of water at as low a level as possible.
The detection of a leak-of-water site has thus far been achieved by a skilled operator at, for example, a valve-mounted site on the water pipe through the listening of the nature of water sound. Since this requires the sense of acute hearing or experiences, it has been usual practices to make such detection at a midnight when there is less external noise, such as vibrations originating from running automobiles on the street.
In the case where the leak of the water out of the water pipe is identified, the operator moves along the water pipe, while holding an acoustic microphone, so as to locate the loudest leak-of-water sound site. If this site is so located, then the operator digs up the most likely area of the ground to see whether or not water leaks out of the water pipe. In this way, necessary repairs are done if the water leaks there.
That is, the detection of a leak-of-water site is so done at such a midnight through the accumulated experiences of the skilled operator, thus very much lowering an operation efficiency involved. It is also difficult to locate that leak-of-water site.